Technological advances in magnetic storage allow data to be stored in ever smaller physical dimension. For example, track widths in magnetic tape or disk storage have become so small that mechanical vibrations which once were irrelevant can now cause writing errors. For example when a read/write head positions itself over a desired track, oscillations on the mechanical structure of the head can be large enough that a write function writes data outside the allowed track width, resulting in write error.
When a read/write head operates, it is moved in a seek operation. This operation locates and moves the head to the proper position for, e.g., writing data. When the seek operation ends and the head is in position, there is a time period during which vibrations in the head must be allowed to settle. To deal with problems of this nature, settling algorithms are typically used which monitor the transient response and attempt to prevent write operations until the settling is completed. Shorter settling times typically permit more errors, while longer settling times, though less error prone, increase access and/or write time for the apparatus. Hence, settling times are typically kept as short as possible while still preventing as many errors as possible.
Non-consecutive settling algorithms employ multiple samples to determine whether settling has occurred. For example, if 2 consecutive position error signal (PES) samples are within 8% of track pitch and the corresponding velocity is within 6% of track pitch, then a settling counter of the algorithm is decreased by one. If this happens a predetermined number of times (e.g., 8 times in some implementations) the settling count reaches zero and settling is considered complete.
While such algorithms greatly decrease write error rate, certain frequency mechanical oscillations can still cause the settling algorithm to fail. For example, seek-induced coil bending resonance creates mechanical oscillations in the range of 900-1600 Hz, which can cause write errors despite the settling algorithm. The consequences of failure lead directly to reliability failure due to data encroachment outside the desired track, caused by data written with marginal PES.
Hence, the present state of the art would benefit from improvements to write operations that further limit these errors without unnecessarily extending the delay in write operations.
The present invention provides a solution to this and other problems.